The present invention relates to a coating apparatus and to a coating method for granular bodies, preferably tablets or pills.
It is possible by means of drum coaters to apply a functional layer in the form of a film layer to pressed tablet cores. This functional layer generally consists of water-soluble monomers in which removal of water and poly reaction are followed by chain formation to give homo- and copolymers. The task of this functional layer is to protect an active ingredient present in the tablet core from the action of light or oxygen, to prevent premature dissolution owing to excessively high ambient humidity during storage, or to allow the active ingredient to show its effect only in particular zones of the digestive tract. Very high quality demands are therefore made on functional layers of this kind.
There are drum coaters in different designs for the coating to be conducted. They can essentially be divided into batch coaters and continuous drum coaters. While application of functional layers by means of batch coaters no longer constitutes a technical challenge, there are still considerable problems in the case of drum coaters in applying a functional layer with uniform thickness on the surface of the tablet. Document WO 2006/108280 A1 describes, for example, a continuous drum coater that achieves the very high demands on layer thickness distribution as necessary, for example, for stomach-resistant film coatings only with a considerable degree of complexity, if at all.